The vote to build what supporters called a "real fence" ¡ª as distinct from the virtual fence already incorporated in the legislation ¡ª was 83-16. The fence would be built in areas "most often used by smugglers and illegal aliens," as determined by federal officials. Sen. Jeff Sessions (news, bio, voting record), R-Ala., estimated the cost at roughly $3.2 million per mile, more than $900 million for 300 miles.

The provision includes a call for construction of 500 miles of vehicle barriers, adding to a system currently in place.

It marked the first significant victory for conservatives eager to leave their stamp on a measure that looks increasingly like it is headed toward Senate passage.

Construction would send "a signal that open-border days are over. ... Good fences make good neighbors, fences don't make bad neighbors," Sessions said. He said border areas where barriers are in place have experienced economic improvement and reduced crime.

"What we have here has become a symbol for the right wing in American politics," countered Sen. Dick Durbin, D-Ill. He said if the proposal passed, "our relationship with Mexico would come down to a barrier between our two countries."

All Republicans and more than half the Senate's Democrats supported the proposal. A core group of bill supporters who have held off other more serious challenges in the past two days made little attempt to fight this one, judging it far less damaging than the attack on the citizenship provision or an attempt on Tuesday to strip out a guest worker program.

Supporters of the Senate measure credited Bush's prime-time Monday night speech with giving fresh momentum to the effort to pass long-stalled legislation.

Across the Capitol in the House, the story was different.

Sensenbrenner's remarks were unusually sharp, given his chairmanship. "He said four times this is not amnesty. Well, it is an amnesty, because it allows people who have broken the law to stay in the country," he said of the positions Bush staked out in his speech earlier in the week.

In a conference call with reporters, Sensenbrenner also said Bush had "basically turned his back" on a tough border security bill after requesting that certain provisions be included before passage last year.

The House legislation passed over strenuous Democratic opposition. It would make all illegal aliens subject to prosecution as felons and calls for construction of a 700-mile fence along the Mexican border ¡ª more than twice as long as the barrier the Senate backed during the day.

Several members of the rank-and-file have criticized Bush for his proposals. To calm their concerns, Rove attended the regular closed door meeting of the rank and file, where participants said he sought to reassure lawmakers about the administration's commitment to securing the borders.